The present invention relates generally to methods and materials for visualization or treatment of vasculature.
Of the estimated 34 million people in the United States who will be age 65 or older in 1995, approximately 1.7 million will have some visual impairment resulting from age-related macular degeneration (ARMD). Approximately 100,000 of those affected will experience a devastating, rapid loss of vision due to choroidal neovascularization (CNV). (See, for example, U.S. Dept. Health and Human Serv., (1994) National Advisory Eye Council (1990-1992).) ARMD is the most common cause of vision loss in people over age 50 and, as the population ages, a greater number of elderly persons will become blind from ARMD than from glaucoma and diabetic retinopathy combined. Leibowitz et al. (1980) 24 Surg. Ophthalmol. (suppl.) 335-610; Sorsby (1972) in: Ministry of Health Reports on Public Health and Medical Subjects (128th ed., London); Ferris (1983) 11 Am. J. Epidemiol. 132-4151.
Clinical research has shown that laser treatment of CNV reduces the risk of extensive scarring in selected cases of CNV characterized by a well-defined, predictable fluorescein angiographic pattern covering an area limited in size. Unfortunately, such xe2x80x9cclassicxe2x80x9d cases comprise only 25% of the population with CNV, leaving 75% of the patients at risk of becoming blind from macular disease without the benefit of laser treatment. Moreover, the frequent (54%) recurrence of CNV is mostly attributed to incomplete angiographic visualization and subsequent inadequate treatment of CNV. Macular Photocoagulation Study Group (1986) 104 Arch. Opthalmol. 503-512. The practical difficulty in detecting CNV clinically has been documented in a recent study involving clinical and pathological examinations of 30 eyes. In 57% of the cases, CNV was detected histologically but not clinically. Sarks (1973) 75 Br. J. Ophthalmol. 587-594. This finding is in agreement with other histopathological studies in which CNV was detected in angiographically-unrecognized lesions. Bressler et al. (1992) 110 Arch. Ophthalmol. 827-832; Small et al. (1976) 94 Arch. Ophthalmol. 601-607.
As presently performed, the ability of fluorescein angiography to highlight CNV is limited by a number of factors. First, the dye rapidly fills both the retinal and choroidal vessels. Thus, visualization of small vascular beds, such as those typical of CNV, is often hampered by the lack of contrast caused by the bright fluorescence emanating from major choroidal vessels. Second, visualization of CNV is based on the leakage into and/or staining of tissue by the dye, which occurs only during a particular pathological stage. This process is not reliable because at certain stages of the disease, diseased vessels do not leak or stain. Also, metabolic waste products may accumulate in the vicinity of the lesion, decreasing the permeability or delaying the leakage into extravascular tissues. Third, when vessels leak, dye accumulates in the tissues surrounding the CNV lesion and actually masks its boundaries. Fourth, both the exciting and fluorescent light may be absorbed by subretinal blood, turbid fluid, pigment, or fibrous tissue, thereby reducing the intensity of the fluorescence emanating from the CNV. Bresler et al. (1988) 32 Surg. Ophthalmol. 375-413; Bressler et al. (1991) 109 Arch. Ophthalmol. 1242-1257.
Indocyanine green (ICG) angiography has been reportedly beneficial in some cases. Destro et al. 96 Ophthalmology 846-853. Because the excitation and emission wavelengths of this particular dye are longer than those of fluorescein, the light penetrates turbid media better, thereby eliminating the fourth limitation mentioned above. On the other hand, however, the enhanced penetration of light in ICG angiography aggravates the first-mentioned limitation of fluorescein angiography, i.e., interfering fluorescence, because large underlying choroidal vessels are visualized more effectively. Moreover, ICG angiography shares with fluorescein angiography the limitation of relying on leakage and staining of extravascular tissues. The poor understanding of the staining and pooling mechanisms of this dye hampers interpretation of angiograms.
The lack of adequate methods of angiographic visualization is unfortunate because clinical research has shown that laser treatment can reduce, in the long term, the risk of extensive loss of vision in classic CNV. (See, for example, Bressler et al. (1991) 109 Arch. Ophthalmol. 1242-1257.) In addition, the failure of laser photocoagulation has been attributed to inadequate identification of the entire extent of CNV and its location relative to the fovea.
As mentioned, CNV is commonly treated by laser photocoagulation in which a thermal scar is produced. The procedure typically causes a dramatic loss of vision when the fovea is treated. See, for example, Macular Photocoagulation Study Group (1991) 109 Arch. Ophthalmol. 1220-1231. Nonetheless, the treatment is performed to prevent progressive visual loss. The cases eligible for treatment, which make up only 25% of the eyes with CNV, must be the well-defined xe2x80x9cclassicxe2x80x9d type of CNV that is not too large. The remaining 75% of affected eyes are untreated because laser photocoagulation does not spare useful vision. In addition, new blood vessels recur in a majority of the patients (54% ) treated with laser photocoagulation, thereby necessitating further scarring treatment. Other than the incomplete identification of CNV mentioned above, recurrence has been attributed to damage to Bruch""s membrane and scarring, conditions known to predispose tissues to new blood vessel growth.
It is an object of this invention to provide methods and materials for selective occlusion of vasculature. That is, it is an object of this invention to provide for the occlusion of blood vessels without significant, concomitant damage to tissue surrounding and supplied by said blood vessels. It is another object of the instant invention to provide methods and materials for selective and non-invasive chemical occlusion of blood vessels and sinuses in the mammalian eye, especially blood vessels and sinuses of choriodal origin. It is a further object of the instant invention to provide methods for selectively and non-invasively occluding vascular abnormalities of the mammalian eye, such abnormalities being associated with macular degeneration and related clinical conditions involving neovascularization, such as choroidal neovascularization. It is still a further object of the instant invention to provide methods for non-invasively occluding vascular abnormalities associated with pathologies of the choriocapillaris such as choroideremia, gyrate atrophy, and acute placoid multifocal pigment epitheliopathy, as well as vascular abnormalities which are non-choroidal such as those associated with diabetes. It is yet another object of the instant invention to provide diagnostic reagents and diagnostic kits for selective, non-invasive chemical occlusion of vasculature. These and other objects and features of the invention will be apparent from the description, drawings and claims which follow.
The present invention provides a method of chemically occluding a blood vessel or blood sinus in a mammalian eye which involves: co-administering intravenously a fluorescent dye encapsulated within heat-sensitive liposomes and a tissue-reactive agent which is effective to cause chemical tissue damage following its activation; non-invasively heating tissue at a pre-determined anatomical locus within the eye so that the heat-sensitive liposomes leak and release their contents into the blood vessel or sinus at the pre-determined locus; exciting the fluorescent dye; visually observing a pattern of fluorescent vasculature which develops at the pre-determined locus; and, activating the tissue-reactive agent disposed within the blood vessel or sinus so that the blood vessel or sinus is chemically damaged to an extent sufficient to occlude the vessel or sinus. As used herein, the steps of the method of the instant invention are collectively referred to as xe2x80x9claser-targeted occlusion.xe2x80x9d In some cases, the steps which precede activation of the tissue-reactive agent are collectively referred to as xe2x80x9claser-targeted angiography,xe2x80x9d xe2x80x9claser-targeted delivery,xe2x80x9d or xe2x80x9claser-targeted visualization.xe2x80x9d The present invention contemplates that the steps of the method of laser-targeted occlusion can be repeated for an amount of time that the liposomes are circulating systemically following their administration. Similarly, the present invention contemplates that the steps of laser-targeted angiography can be repeated for an amount of time that the liposomes are circulating systemically following their administration.
In another embodiment of the method of the instant invention, the method of chemically occluding a blood vessel or sinus in a mammalian eye involves: co-administering intravenously a fluorescent dye and a tissue-specific factor co-encapsulated within heat-sensitive liposomes, said tissue-specific factor being effective to impair growth or regeneration of vasculature; non-invasively heating tissue at a pre-determined anatomical locus within the eye so that the heat-sensitive liposomes leak and release their contents into the blood vessel or sinus at the pre-determined anatomical locus; exciting the fluorescent dye; visually observing a pattern of fluorescent vasculature which develops at the pre-determined anatomical locus; and, exposing the blood vessel or sinus at the locus to the tissue-specific factor disposed within the blood vessel or sinus so that the growth or regeneration of the blood vessel or sinus is impaired.
In yet another embodiment, the instant invention provides a method of occluding vasculature in a mammalian eye which involves: administering intravenously heat-sensitive liposomes having a fluorescent dye encapsulated therein; irradiating a pre-determined anatomical locus within the eye with a first laser beam to selectively and non-invasively heat the vasculature at the locus so that the liposomes accumulated at the locus release their contents into the vasculature at the locus; identifying a blood flow origin within the vasculature by visualizing an advancing blood/dye boundary within a feeder blood vessel that supplies blood to a vascular abnormality at the locus; and, occluding the feeder blood vessel with a second laser beam focused on the blood/dye boundary.
In another aspect, the invention features materials for use in the method, e.g., a diagnostic reagent and a diagnostic kit each comprising a fluorescent dye encapsulated within heat-sensitive liposomes and a tissue-reactive agent. Alternatively, the diagnostic reagent and kit each comprise a tissue-reactive agent co-encapsulated with fluorescent dye within heat-sensitive liposomes. In yet another embodiment, the instant invention contemplates that the diagnostic reagent and kit each comprise a fluorescent dye which is a tissue-reactive agent. The diagnostic kit of the instant invention optionally further comprises means for encapsulating fluorescent dye, either alone or together with tissue-reactive reagent, within heat-sensitive liposomes.
The method of laser-targeted angiography and occlusion of the instant invention solves problems encountered in conventional fluorescein or ICG angiography. For example, the local selective release of a fluorescent dye according to the method of the instant invention permits pre-determined vascular beds to be visualized without interference from fluorescence emanating from overlying or underlying beds. Second, visualization according to the instant invention is independent of staining and leakage of dye into tissue surrounding a region of abnormal vasculature, such as choroidal neovascularization (CNV). Rather, it relies solely on the presence of a dye in the vascular lumen. Thus, the CNV can be visualized as long as it is patent, i.e., open to blood flow. This feature also simplifies interpretation of angiograms. Third, the short time during which release of the encapsulated dye occurs, accompanied by rapid and eventual clearance thereof, ensures that the dye does not accumulate outside the vessels, and thus does not mask the CNV as do conventional materials and methods. Fourth, the hemodynamics of the CNV, delineated by the progress of the dye, using the methods of the instant invention, allow the vessels feeding the CNV to be identified. Such identification allows the clinician to selectively occlude an identified feeder vessel. In this manner, large areas of retina overlaying the CNV could be spared, thus limiting the unnecessary visual loss typically associated with prior art methods of photocoagulation. Fifth, angiograms performed in accordance with the instant invention can be repeated for at least about 45 minutes as long as the liposomes are circulating in the blood. This provides opportunities to correct errors in alignment of optical equipment and to perform angiography of both eyes during the course of a single patient visit and/or single therapeutic procedure.
All the above advantages can be demonstrated using the methods and materials of the instant invention which permit successful visualization of classic and occult CNV, as well as visualization of the choriocapillaris, even in the presence of scar tissue. Laser-targeted angiography as described herein detects and delineates CNV and CNV-type lesions effectively. This increases the number of patients who could benefit from such therapy, reduce the recurrence rate now attributed to lack of adequate visualization, and restrict the treated area, thereby reducing the amount of visual loss accompanying occlusion treatment.
As disclosed herein, a method of occluding CNV that does not cause a scar and spares the overlying retina and adjacent choriocapillaris is highly desirable and can be met by the instant invention""s methods of laser-targeted occlusion. In one embodiment, the method of the instant invention combines laser targeted delivery and photodynamic therapy by targeting delivery of a photosensitive agent to the CNV and occluding the CNV by photosensitization of the agent. Such a method solves many of the limitations of systemic photodynamic therapy and those of conventional thermal laser photocoagulation. Thus, the tissue-reactive agent can be released specifically in the choroid, thus avoiding release in the retinal vessels. Similarly, the agent also can be released within the CNV while avoiding release in the retina. Next, by irradiating only after the agent""s release into the pre-determined anatomical locus, tissue damage can be limited essentially to the vessels that are selectively perfused by the agent. The lack of accumulation of the agent in the interstitial tissues prevents their subsequent damage upon activation. Third, as disclosed herein, there are clear indications that CNV""s are perfused by a slower blood flow than the normal choriocapillaris. Therefore, the agent could be released and the tissue irradiated only after enough time has elapsed to ensure clearance from the normal choriocapillaris. This sequence would preclude damage to the choriocapillaris which is crucial to the maintenance of the retinal pigment epithelium. Fourth, laser-targeted occlusion of CNV according to the instant invention allows both xe2x80x9cclassicxe2x80x9d and xe2x80x9coccultxe2x80x9d type lesions to be amenable to treatment, as the skilled practitioner now can selectively occlude the CNV while sparing the retina and thus preserving vision. Fifth, laser-targeted occlusion does not cause a scar as does thermal occlusion, thereby reducing risk of recurrence of neovascularization.
The foregoing and other objects, features and advantages of the present invention will be made more apparent from the following detailed description of preferred embodiments of the invention.